1. Field of the Invention
The present invention relates to a process for preparing a poly(alkylene oxide) by polymerizing an alkylene oxide. The poly(alkylene oxide) is an important polymer which is used as a raw material of polyurethane foam, elastomer, etc. by reacting with an isocyanate compound or a surfactant.
2. Description of the Prior Art
In the preparation of a poly(alkylene oxide) by polymerizing an alkylene compound, it is most popular that the hydration reaction between an active hydrogen compound such as polyhydric alcohol and a basic alkali metal compound such as potassium hydroxide is conducted before the initiation of the polymerization to form an alkali metal salt of the active hydrogen compound, which is used as an initiator. This process has already been put into practical use, industrially. With respect to a combination other than this combination of the initiator, U.S. Pat. No. 3,829,505 discloses that a polymer of propylene oxide is obtained by using an active hydrogen compound and a compound represented by Zn.sub.3 [Fe(CN).sub.6 ].sub.2.H.sub.2 O.dioxane. Japanese Patent Kokai (Laid-Open) Publication No. 276821/1990 discloses that a polymer is obtained by reacting a polyol prepared in the presence of a zinc hexacyanocobaltate complex with sodium methylate and polymerizing the reaction product with ethylene oxide. Japanese Patent Kokai (Laid-Open) Publication No. 232433/1987 discloses that a polymer is obtained by polymerizing ethylene oxide using a product obtained by adding a hexane solution of diethylzinc to a dispersion prepared by adding 1,4-butanediol and a nonionic surfactant to a hexane slurry of fumed silica. However, all of these polymers contain metallic components and an adverse influence is exerted on the reaction in the preparation of a polyurethane or physical properties of the polyurethane when these metallic components are remained in the formed poly(alkylene oxide). Therefore, in the preparation of the polyalkylene oxide, a special process or complicated step of sufficiently removing these metallic components is required.
In Japanese Patent Kokai (Laid-Open) Publication No. 159595/1975, a polymer of ethylene oxide is obtained by using, as a metal free initiator, a combination of an alkanepolyol as the active hydrogen compound and an ether adduct of boron trifluoride. Also with respect to this initiator, however, it is known that impurities in the polymer exert an adverse influence on physical properties of the polyurethane and, therefore, a complicated step is required to sufficiently remove impurities. In Japanese Patent Kokai (Laid-Open) Publication No. 12026/1982, a polymer of an alkylene oxide is obtained by using alcohols and aminophenol. In Japanese Patent Kokai (Laid-Open) Publication No. 38323/1981, a propylene oxide is polymerized by using sorbitol and tetramethyl ammonium hydroxide. However, all processes have a problem that a polymerization activity is insufficient and an odor of an amine compound is remained.
There has also been known a process for preparing a poly(alkylene oxide) by polymerizing an alkylene oxide compound in the presence of a phosphazene compound and an active hydrogen compound (EP0763555; Macromol. Rapid Commun., Vol. 17, pages 143-148, 1996; and Macromol. Symp., Vol. 107, pages 331-340, 1996).
The phosphazene compound in this process is an initiator having strong basicity, but is not at all industrially advantageous because a complicated step is required to synthesize the phosphazene compound and a stronger basic compound must be used to afford strong basicity. There is also a problem on handling that the phosphazene compound is liable to cause a change of properties by a carbon dioxide in an air because of its strong basicity.
EP0791600 discloses a process for preparing a poly(alkylene oxide) by substantially polymerizing an alkylene oxide compound in the presence of a phosphazenium salt of an active hydrogen compound. This process requires that the phosphazenium salt of the active hydrogen compound is formed by the dehydration or desalting reaction of a phosphazenium hydroxide with an active hydrogen compound or of a phosphazenium halide with an alkaline metal salt of the active hydrogen compound before the initiation of the polymerization. An inorganic salt or water formed in that case can inhibit smooth proceeding of the polymerization, sometimes, and it becomes complicated to remove the inorganic salt and, therefore, an improvement is industrially required.